1. Field of the Invention
This invention relates to device packaging, for example packaging for a high power optical coupling device.
2. Description of Related Art
In optical communications systems, cladding-pumped fiber devices are important in a variety of applications, for example as amplifiers and lasers. Cladding-pumped fiber devices comprise a cladding-pumped fiber having a single mode core and at least one cladding layer. A major advantage of the cladding-pumped fiber is that it can convert light energy from low brightness sources which is coupled into the cladding of the cladding-pumped fiber into light of high brightness in the core. In a cladding-pumped laser or amplifier, the core is doped with a rare-earth dopant, such as erbium. The pump light in the cladding interacts with the core and is absorbed by the rare-earth dopant. If an optical signal is passed through the pumped core, it will be amplified. In the case of the cladding-pumped laser, the cladding pumped fiber will act as a laser oscillator and convert the pump light to a desired wavelength.
A difficulty preventing full exploitation of cladding-pumped fiber devices involves the problem of efficiently coupling a number of low brightness sources into the cladding of the cladding-pumped fiber device. A common approach is to couple the light from a diode array, such as broad-stripe semiconductor lasers, into multimode fibers using bulk optics to couple the light from the multimode fibers into the cladding-pumped fiber. Another approach involves an optical coupling device which couples light from a diode array, such as a plurality of semiconductor emitters, to a cladding-pumped fiber via tapered fiber bundles fusion-spliced to the cladding pumped fiber. However, in these approaches where light energy of relatively high power (for example, greater than 1 Watt) is being coupled together, the light energy escaping from the optical coupling device can damage the optical coupling device or other devices.
Conventional packaging for optical devices does not adequately protect the higher power ( greater than 1 Watt) optical devices against the escaping light energy. Typically, optical devices handle less than 1 Watt of light energy and operate satisfactorily being mounted on metal, glass or ceramic. However, if a high power optical coupling device is mounted on ceramic or metal, the light energy that leaks out can be absorbed by the ceramic or metal and be converted to thermal energy which can damage the optical coupling device, for example by melting or burning up the optical coupling device or by breaking the optical coupling device because of the expansion or contraction of the ceramic or metal due to changing temperature. Using glass packaging for the optical fiber device can solve some of these problems, but the glass packaging is more fragile, and the light energy can escape from the device to potentially damage or interfere with the operation of other devices.
The present invention provides a packaging system including a medium which transports energy in a first form away from a radiation point in a device to where the energy can be converted to a second form without damaging the device or effecting other devices. In certain embodiments, the medium can inhibit the propagation of energy in the second form. For example, in an optical coupling device, the medium includes a substrate adjacent to the radiation point which transports light energy away from the radiation point to a housing which converts the light energy into thermal energy away from the radiation point. In certain embodiments, the substrate can inhibit the transmission of thermal energy, thereby further protecting the optical coupling device from the thermal energy. Thus, the effect of the thermal energy on the operation of the optical coupling device is reduced as well as the effect of the escaping light energy on other devices.
In accordance with an aspect of the present invention, at least a portion of the device is suspended from a substrate, for example, to protect the device against a third form of energy. For example, in the optical coupling device, the medium includes an air gap which separates the radiation point from the substrate to suspend at least a portion of the device. The air gap enables the device to be protected against the mechanical energy resulting from the expansion or contraction of the packaged device due to changing temperature. In certain embodiments, the housing is provided with at least one opening in which a pliable seal is inserted which can absorb the mechanical energy resulting from the expansion or contraction of the packaged device due to changing temperature. The pliable seal can also prevent light energy from interfering with other devices.